First...check Event Viewer for any errors which cite "ATAPI" or "disk0, disk1, etc.".
If found, post the details.
You can also try deleting the upper/lower filters.
Upper & Lowe Filters - http://delltrain.wordpress.com/2008/07/15/...d-lower-filter/
Upper & Lower Filters - http://support.microsoft.com/kb/316529
Upper and Lower Filters. CD-ROM 314060 - http://support.microsoft.com/kb/314060
Caution: Before doing any registry edit, back up your registry. Even though the above is a common cure for various situations, backing up the registry should be accomplished before doing any registry edit.
Excellent tool for such: ERUNT Registry Backup Tool - http://www.snapfiles.com/get/erunt.html